The present disclosure relates to a hydraulic control device for an automatic transmission that is suitable to be mounted on a vehicle or the like.
Automatic transmissions that use a belt-type continuously variable speed change mechanism that includes a pair of pulleys and a belt (or a chain) wound around the pulleys and made of metal and that continuously varies a speed by changing the effective diameters of the pulleys have been widespread as automatic transmissions that are suitable for use in vehicles, for example. There have also been known automatic transmissions that use a toroidal-type continuously variable speed change mechanism or a cone-ring-type continuously variable speed change mechanism, besides the belt-type continuously variable speed change mechanism.
There has further been developed an automatic transmission that has two parallel power transfer paths, namely a first power transfer path that couples an input shaft and an output shaft to each other via a forward/reverse switching device and a second power transfer path that couples the input shaft and the output shaft to each other via a continuously variable speed change mechanism (see WO 2013/176208). In the automatic transmission, the forward/reverse switching device has a first clutch to be engaged only during forward travel and a brake to be engaged only during reverse travel, a meshing clutch with a synchronization mesh mechanism (hereinafter referred to as a “meshing clutch”) is provided in the first power transfer path, and a second clutch is provided in the second power transfer path.
In the automatic transmission, when the vehicle starts to travel in the forward direction or when the vehicle travels forward at a speed that is less than a predetermined speed, a forward non-continuously-variable mode in which the vehicle travels using a low forward speed without performing continuously variable speed change with the first clutch and the meshing clutch in the engaged state and with the second clutch in the disengaged state is entered so that drive torque from a drive source is transferred from the input shaft to the output shaft through the first power transfer path. When the vehicle travels forward at a speed that is not less than the predetermined speed, meanwhile, a forward continuously-variable mode in which the second clutch is in the engaged state and in which the first clutch and the meshing clutch are in the disengaged state is entered so that drive torque from the drive source is transferred from the input shaft to the output shaft through the second power transfer path. When the vehicle travels in reverse, further, a reverse non-continuously-variable mode in which the brake and the meshing clutch are in the engaged state and in which the first clutch and the second clutch are in the disengaged state is entered so that drive torque from the drive source is transferred from the input shaft to the output shaft through the first power transfer path.
In the automatic transmission, in addition, in the case where a shift lever is switched to a reverse range during forward travel at a predetermined speed or more, control is performed so as not to engage the brake not to establish a reverse speed, in order to protect a power transfer mechanism.